Pathogenicity of Alternaria tagetica on Tagetes. Elizabeth Small Wood Hotchkiss, Former Graduate Research Assistant, Department of Plant Pathology and Physiology, Clemson University, Clemson, SC 29631. Luther W. Baxter, Jr., Professor, Department of Plant Pathology and Physiology, Clemson University, Clemson, SC 29631. Plant Dis. 67:1288-1290. Accepted for publication 25 July 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-1288.

Blight of marigold (Tagetes erecta and T. patula) caused by Alternaria tagetica is characterized by dark lesions on leaves, stems, and petals. The pathogen did not cause symptoms on six other species of Asteraceae. Symptom severity increased with longer periods of high moisture after inoculation. The pathogen was isolated from commercial marigold seed. A. tagetica formed abundant mycelial growth on carrot-juice agar, potato-dextrose agar, and oatmeal agar. The number of spores produced by the pathogen was increased when oxythioquinox (100 mg a.i./L) was added to the medium and incubated under alternating periods of light and dark at 25 C.